In a radio communication system, the quality of the signal received by a User Equipment (UE) depends on the channel quality and the noise intensity of a serving cell and the interference intensity of neighboring cells. When certain transmitting power is given, in order to optimize the capacity and the coverage of a system, the transmission rate of a transmitter should go to match the channel capacity of each user to the greatest extent, that is, a UE sends more data when the quality of the signals received is good and sends less data when the quality of the signals received is poor. The transmission rate is changed by adjusting a Modulation and Coding Scheme (MCS). A low-order MCS is used when the channel quality is poor so as to tolerate interference and noise of higher intensity, however, the transmission rate is low in this case. A high-order MCS, by which high transmission rate can be achieved, is sensitive to interference and noise and is therefore employed when the quality of a channel is good. This technology is called Adaptive Modulation Coding (AMC) based link adaptation technology.
In a Long Term Evolution (LTE) communication system, an eNodeB selects a suitable modulation scheme and a proper coding rate according to a Channel Quality Indicator (CQI) fed back by a UE so as to improve the transmission rate and the throughput of the system. The CQI is a supportable data rate indicator given after taking the signal-to-noise ratio (SNR) level of the current channel and the performance of a receiver into consideration. The selected CQI is calculated based on the quality of a downlink received signal. It should be noted that a CQI is the highest-order MCS capable of guaranteeing a Block Error Rate (BLER) not to exceed 10% in the condition of the current channel and noise, rather than a direct indicator of a downlink Signal-to-Noise Ratio (SNR).
In the conventional technologies, as a wireless channel has a frequency selective fading characteristic in a multi-path channel and the SNR of each sub-carrier is different in an OFDM based multi-carrier communication system, it is complicated to calculate a CQI.